Juddian:
Last time i drove a David Brown box it was in (if i recall correctly) a Sed Ack 400 6 wheeler rolonoff.
I’d previously had one in a SedAck 400 Artic with a 250 ■■■■■■■ lump.As i recall it was a simple 6 speed constant mesh box, but in most cases was back to front in the way you selected gears, with 1st being where you would expect 6th to be, over to you and back, and 6th where 1st should have been.
Once on the move you didn’t need to bother with the clutch just get the revs right for the next gear and it would slot in cleanly, you could do this with many constant mesh boxes.Point of interest as you mentioned at one time David Brown owned Aston Martin, presumably when it was still based at Newport Pagnell.
The 400 6 wheeler had PTO for operating the Multilift hooklift gear, whoever fitted it managed to run it off 5th gear, hence it was so high geared you could load the body in about 15 seconds, course this put tremendous strain on the box and the casing split pouring all the oil out in a council yard, my mate tried his best to be gentle with it so much so that once the PTO actually stalled the engine which saw the Gardner XLC fire up running backwards.
Quite a number of different boxes were back to front as it were, Daf 2600 had a 12 speed ZF (95% sure it was ZF) splitter that was also back to front and that same box i also came across in a Daf 2800DKTD, but the gears might have been the right way round by then, memory isn’t what it once was.
I’m reasonably sure (I think… 
) I’ve heard of 8-speed DB boxes in some wagons. I might be wrong (again).